1. Field of the Invention
This invention relates to a disc reproducing apparatus and more particularly, is suitable for applying to a system in which audio signals recorded on a magneto-optical disc are reproduced.
2. Description of the Related Art
Heretofore, there have been proposed a disc reproducing apparatus which can reproduce the data from both of a magneto-optical disc and an optical disc, and a disc recording/reproducing apparatus which can record a desired information on a magneto-optical disc repeatedly.
Meanwhile, in the case that the disc reproducing apparatus is used for reproducing the audio data recorded on the magneto-optical disc, etc., since it can be considered that the disc reproduction device is often used outdoors which is apt to receive vibration from the outside, a technology is known, for example, in U.S. Pat. No. 5,214,631 to improve the anti-vibration strength by using a semiconductor memory in order not to interrupt a data read and cause tark jump if the large vibration is given to the disc reproducing apparatus.
In this vibration protection technique, the audio data, which is compressed to about 1/5 by a sound compression technique, error correction processed, and recorded, is read out from the magneto-optical disc at the rate of 1.4 [Mbit/s], and the decoded audio data is written in a random access memory (hereinafter, referred to as "RAM") temporarily.
Thereafter, the audio data being compressed is read out from the RAM at the rate of 0.3 [Mbit/s] continuously and is expanded to the former data length, so that the data of specific size is reproduced while it is continuously stored in the RAM. Thus, the anti-vibration strength is improved. That is, during this time, the audio data is read from the magneto-optical disc intermittently.
In this way, by storing the audio data to be actually reproduced in the random access memory to the data several seconds ahead, if the data can not be read out due to a large vibration, the stored data is reproduced until the data read starts again. Therefore, the occurrence of tark jump can be prevented previously.
Meanwhile, the magneto-optical disc used for the reproduction of this audio data is arranged into a data recording area for recording the audio data which divides into specific block units (hereinafter, referred to as a "sound group") for every data unit (hereinafter, referred to as a "cluster"), and a read-in area for recording the table of contents information (TOC data) which includes disc information and track information excluding the music data.
The data recording area among these is allocated in the outside of the recording area, and the read-in area is allocated in the inner periphery of the recording area. The write and read of data to the data recording area is performed at an integer multiple of one cluster.
Here, one cluster is composed of 36 sector data. In the magneto-optical disc for recording, the head three sectors are allocated to a link sector L as a redundant sector, the next one sector to a sub-data S, and the other 32 sectors to compressed data (FIG. 1A).
More specifically, one sector is composed of 12 bytes of a sync area, 4 bytes of a header area, 4 bytes of a sub-header area, and 2332 bytes of a compressed data area. To the header area from the head, 2 bytes for a cluster number, 1 byte for a sector number, and 1 byte for a mode area is respectively allocated (FIGS. 2A and 2B).
To one sector in the compressed data area, 5.5 pairs of sound groups composed of two sectors (even sector, odd sector) and each of sound group composed of two channel data (a left channel data or a right channel data) and 5.5 pairs of sound groups are allocated (FIGS. 1B and 1C).
In this type of disc recording/reproducing apparatus, 1 sound group of the compressed data of 512 samples, i.e., 424 bytes, is handled as one unit (FIG. 1D).
This type of data structure is known, for example, in U.S. pat. application Ser. No. 48359 filed Apr. 15, 1993, now U.S. Pat. No. 5,363,362.
In the disc reproducing device, the audio data read from the magneto optical disc is written in the RAM following the procedure shown in FIGS. 3 and 4.
That is, a micro computer (hereinafter, referred to as "CPU"), which constitutes the system controller of the disc reproduction device, when it enters the audio data read out routine (step SP1), initializes a count value (step SP2) so that the data is read at a predetermined address of the RAM, and then, accesses to a predetermined data area and starts to read out the data (step SP3).
After this, the CPU observes the existence of the sync interrupt (step SP4), and then at the time of interruption, judges whether the mode is the write mode or not (that is, the write mode or the monitor mode) (step SP5).
Next, when the present mode is the monitor mode (that is, the case where a negative result is obtained), the CPU judges whether the sector which is presently read from the header data becomes the sector just before the waiting target sector (step SP6). Then, if it is not the sector just before the target sector, the CPU judges whether the immediately preceding mode is the write mode or not (step SP7), and in the case where it is the write mode, the CPU returns to step SP4 and repeats the above processing.
On the contrary, when the sector just before the target sector is detected, the CPU sets the count value to specify the RAM address, and at the same time, switches the write/monitor mode switching flag WRMN to the "H" level, returns to step SP4, and waits for the input of the target sector (step SP8 and step SP9).
The write/monitor mode switching flag WRMN is the flag which permits the transition to the write mode when the sync with "H" level is inputted. And the write/monitor mode switching flag WRMN is handled as the flag which permits the transition to the monitor mode when the sync with "L" level is inputted.
When the CPU detects the sync interrupt in the state that the target sector is inputted (step SP4 and step SP5), the CPU proceeds to the write mode and starts to write the data in the address and judges whether the write mode is to be terminated after reading out the present sector or not (step SP11).
In the case where the writing of data is to be terminated after reading out the present sector, the write/monitor mode switching flag WRMN is switched to the "L" level (step SP12). However, the CPU generally proceeds to step SP13 directly and judges whether the sync interrupt is just after the transition to the write mode or not.
Here, the CPU proceeds to step SP14 in the case that the interruption is just after the transition to the write mode, and confirms whether the header is correct or not. Then, if the header is correct, the CPU returns to step SP4 and waits for the next sync interrupt.
On the contrary, when the header is not correct, the CPU switches the write/monitor mode flag WRMN to the "L" level, sets the target sector again (step SP15 and step SP16), and returns to SP4 to process again from the monitor of the target sector.
Further, when a negative result is obtained in step SP13 including the case where a positive result is obtained in step SP7, the CPU judges whether or not an error has occurred in the sector data written just before (step SP17).
When an error has occurred, as the same as described above, the CPU switches the write/monitor mode switching flag WRMN to the "L" level, sets the target sector again (step SP19 and step SP20), and returns to step SP4 in order to read out the correct data again.
On the contrary, when an error has not occurred, the CPU judges whether the present mode has already moved to the monitor mode or not. In the case that it is in the monitor mode, the CPU proceeds to step SP22 and terminates the processing, whereas in the case that it is in the write mode, the CPU returns to step SP4 to continue the processing.
In this way, the preceding sector has to be detected to permit the write (step SP6) and three confirmations of whether the target sector is actually read, whether the header is correct (step SP14), and whether the data is written correctly are required for writing the specific sector in the predetermined address of RAM.
However, the judgement process is complicated as described above, and moreover, when an error occurs, the process of setting again the read out of the data into the RAM and the access to the RAM is required in addition to the above three confirmation processing. Therefore, the load for the CPU is large.